Effects of Asphalt Foaming on Damage Characteristics of Foamed Warm Mix Asphalt

Abstract

In the asphalt foaming process, the foaming water content (FWC) controls the formation and characteristics of water bubbles. These water bubbles are expected to be expelled from the foamed warm mix asphalt (WMA) during mixing and compaction. However, foaming water may not be completely expelled, rather some of the microbubbles may be trapped in the foamed WMA even after compaction. These microbubbles, or undissipated water, can diffuse over time and cause damage to the foamed WMA. To this end, this study has determined the effects of foaming on the fatigue, moisture damage, and permanent deformation characteristics of foamed WMA. Foamed asphalt and mixtures were designed with varying FWCs and they were tested using linear amplitude sweep, multiple stress creep recovery, four-point flexural beam, and Hamburg wheel tracking tests. Primarily, asphalt foaming dynamics were assessed with a laser-based non-contact method. A simplified viscoelastic continuum damage concept and a three-phase permanent deformation model were used for damage evaluation. The study reveals that foaming softens the binder, which results in slightly higher rutting and moisture susceptibility, though an equivalent or slightly improved fatigue characteristic compared with the regular hot mix asphalt.

Evaluation of Rutting, Fatigue, and Moisture Resistance of Low-Energy Asphalt Mixtures Modified by Crumb Rubber

“…In this method, the failure point N S×n ð Þ occurs when the S × n curve reaches its maximum value according to the load cycle. In this situation, the microcracks are transformed into macrocracks by changing their form [42].…”

Evaluation of Full-Depth Reclamation and Cold Central-Plant Recycling Mixtures for Laboratory Compaction, Mechanistic Response, and Performance Properties

“…A linear variable displacement transducer measures the rut depth at 11 points along the wheel passing direction with 0.01 mm precision. There are several different methodologies to analyze HWT testing data to evaluate rutting and stripping (23)(24)(25)(26)(27).…”

A Study of Adhesion in Foamed WMA Binder-Aggregate Systems Using Boiling Water Stripping Tests

“…The majority of the works focus on the functional properties of the foamed binders, mostly showing no significant detrimental effects of the foaming process; however, decreased aging of the binders is often raised as a potential problem for the short-term high-temperature performance of these mixtures [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. A number of studies have been published on the resistance to moisture damage of warm-mix-asphalt produced using mechanical water foaming, showing that these mixtures may be more susceptible to the action of water [ 43 , 44 , 45 , 46 ]. In some studies [ 44 ], it was also shown that plant-produced foamed warm-mix asphalt exhibits similar moisture susceptibility to hot-mix asphalt, as opposed to laboratory-produced warm mixes.…”